This week, we explore the problem of persistent pain. We find out how chronic pain is currently treated, and look to our DNA for the genetic clues that could lead to future painkillers. In the news, a new TB vaccination that stands out on it's own, how babies make sense of broken toys, and why flying in a flock may be exhausting for pigeons. Plus, in Question of the Week, Diana asks why we have a spare copy of some organs.